Only remove credentials

app/src/main/java/com/mylloon/mobidl/Credentials.kt

@@ -110,7 +110,8 @@ class Credentials {
         // clear shared pref
         val sharedPref = context.getSharedPreferences(sharedPref, MODE_PRIVATE)
         with(sharedPref.edit()) {
-            this.clear()
+            this.remove("username")
+            this.remove("password")
             this.apply()
         }
     }